Communication controller for an active transponder

ABSTRACT

A method for processing of encoded information by a battery-powered active transponder is disclosed for the application within a transponder system for the wireless payment of road toll having the steps of receiving modulated microwave radiation of preset frequency by the transponder over the antenna and for obtaining an input signal demodulated for obtaining a binary input data sequence, feeding said binary input data sequence to a digital processor (microcontroller) operated by a processing clock of preset clock frequency for decoding and generating of a binary output data sequence, and forming an output signal from an answer to the received input signal within a certain duration.

The invention concerns a method according to the introductory part ofclaim 1 as well as a communications controller according to theintroductory part of claim 6.

BACKGROUND OF THE INVENTION

The background of the invention is the wireless payment of charges forthe use of roads (road toll) by vehicles. Systems provided for thispurpose have been delivered by the Q-Free ASA company since many years.Nowadays these systems are used in Norway and are well known under theterm “Q-Free-box”. In this connection the term “box” is related to themodule of this system attached to an individual vehicle, that is to sayto a so-called transponder. This transponder receives data from a mainstation of the transponder system and as an answer on this transmittsindividual data back to the roadside. Meanwhile the technologicaldevelopment in this field has turned to transponders which—contrary totransponders formerly used in this field—are being operated not passive,but active and for the operation of which microwave radiation withfrequencies in the range of 5.8 GHz is applied. With this knowntransponder system the radiation received by the transponder isamplitude modulated for the transmission of data, while the microwaveradiation transmitted by the transponder for the transmission of data isphase modulated.

The modulated input signal obtained in the transponder by the receptionof the microwave radiation initially is demodulated for obtaining abinary input data sequence (of an input data frame). Then this inputdata sequence is fed to a digital processor (microcontroller) operatedby a processing clock of preset clock frequency for decoding and furtherprocessing of the received data as well as for generating of a binaryoutput data sequence (output data frame). During a certain duration fromthe output data sequence as an answer to the input signal an outputsignal is formed in the transponder which as modulated microwaveradiation of certain frequency is irradiated over the antenna of themicrocontroller.

These active transponders are as energy source provided with a battery.In this connection the term “battery” comprises electrical primary cellsas well as electrical secondary cells in a single oder in a multiplearrangement.

With the known transponder systems the succeeding transactions(transaction sequencies) between the main station of the transpondersystem and the individual transponder are carried out on the basis of anadvanced communications protocol (HDLC-High Level Data Link Control) andusually contain the processing of data sequencies and control fields.Furthermore there is a considerable need for the security of thetransactions which are to be carried out. To the most common securityalgorithms belong DES (Data Encrypting Standard System) and Trippel-DES.However the application of these security algorithms usually means thatwith this the processing of data by the transponder becomes very timeconsuming.

To this day the most common solution for a transponder of thetransponder system is a solution, with which a serial processor isapplied as microcontroller. With this solution there is availableflexibility for changes and it is possible to achieve satisfyingtransaction speed with the use of processors, which operate with asystem clock rate with a clock frequency of 10 MHz and higher.

The greatest problem which consists with microcontrollers applied ascommunications controllers until now is that there from the relativelyhigh clock frequency of the system clock results a relatively high loadfor the battery of the transponder, and this in view of the averageheight and the duration of the current (integral over the current pulsesover the time withdrawn with the frequency of the system clock) as wellas in view of the fact that the pulse-like occuring current withdrawalrepresents an exceptional load for the battery. Even if this currentwithdrawal does not mean so much for the life time of the components ofthe transponder so a current withdrawal of such an extent and id anespecially pulse-like occuring way is problematical particularly atrelatively low temperatures where the internal resistance of the batteryis high.

Finally the microcontroller applied for the transponder until now is aserially operating processor. This means that such a processor is notideal in view of the processing of data which can be processed parallel,especially not then when on the one hand processing-wise extensibleactions (decoding) are necessary in the processor and on the other handwithin a shortest possible duration after receipt of the input signal anoutput signal shall be emitted from the transponder.

Object

The invention has the aim on the one hand to considerably reduce thementioned load of the battery for extending its life time and forimproving its operability and on the other hand to enable thetransponder to emit an output signal onto the received input signalwithin a relatively short duration.

Invention

For achieving the aforementioned aim the invention according to thecharacterizing part of claim 1 and 6 respectively is proposed.

Further advantageous and suitable procedural steps or measures areindicated in claims 2-5 and 7-9.

On the basis of the knowledge that with the transponder system inquestion the structure of the content of the data sequences received andtransmitted by the transponder at least at a considerable amount allowsa parallel and particularly bit-by-bit occuring processing, the solutionfor carrying out procedural steps according the invention indicated inclaim 1 compared to the nowadays state-of-the-art offers the advantageof a considerable reduced load of the battery of the transponder bypulse-like occuring current withdrawal together with a relatively shortduration until irradiation of an answer onto the received input signal.

An advantageous feature of the invention according claim 1 is indicatedin claim 2. With a parallel processing of data of the decoded input datasequence carried out correspondingly it is possible to realize thisprocessing with a system clock rate with only a fraction of the clockfrequency usual until now and nevertheless compared to the previoussolution to considerable shorten the duration between the receiving ofthe input signal up till the the forming of the output signal. For thatonly the extent of the processing of data of the input data sequence nowoccuring has to exceed the extent of the reduction of the clockfrequency in its impact onto the mentioned duration. For generating ofsuch a-compared to the state-of-the-art “slower”—processing rate acorresponding oscillator can be applied in the transponder.

Advantageously the procedural step according to claim 3 is applied. Thissolution is useful in view of the fact, that the symbol clock is thatclock within the transponder system, which has the lowest clockfrequency, namely a considerably lower clock frequency compared to theprevious system clock. The application of a separate oscillator withinthe transponder for generation of the system clock for the processor canbe done without. This also has a positive effect on the load of thebattery.

By retrieving the symbol clock and the following use of it as systemclock an ideal solution for the current withdrawal from the battery isobtained. The symbol clock is that clock with the absolutely lowestclock frequency which can be obtained in the transponder system withoutintroduction of additional buffers or the like. A microcontrollersolution which is based on a plurality of processor modules, which arebeing operated with this system clock, enables bit-by-bit occuringdecoding of the data reaching the transponder. This forms a contrast toa microcontroller solution, with which at first the data sequence (thedata frame) has to be stored and thereafter the processing of the datacan be started. claim 4 indicates a preferred solution for forming of aclock frequency derived from the clock frequency of the symbol clocktiming generator or corresponding to this clock frequency.

In view of the aforementioned knowledge of a processibility of thementioned data in a more or less parallel occuring mode claim 5indicates a particularly useful procedure.

The claims 6-9 concern a communications controller or useful design ofit as it can be applied with advantage in connection with the methodaccording to the invention.

EXAMPLES

In the following the invention will be described more detailed with theaid of FIG. 1 and 2 of the drawing.

FIG. 1 shows in connection with the invention an essential part of acommunications controller of a transponder according to thestate-of-the-art and as a block diagram and

FIG. 2 shows essential parts of a communications controller as it isapplied in connection with the invention and as a block diagram.

FIG. 1 shows a communication controller 11 of a transponder not shown infurther detail according to the state-of-the-art. The system clock forthe communications controller 1 is being delivered by an oscillator 12.Over a line 13 incoming input data are being stored in a receivingmemory (buffer) 14. When the complete data sequence (data frame) isbeing received and stored, the processor core 15 will start theprocessing of the input data and prepare an answer of the transponderonto the input data. This happens with a system clock with a clockfrequency of about 10 MHz or with a still higher clock frequency. Afterthe answer is completed it will be laid down in a transmission buffer16, and as soon as the transmission buffer 16 is filled with data thetransmission of data can be started and the answer can be irradiatedover the antenna of the transponder in the form of a phase modulatedmicrowave radiation.

FIG. 2 shows essential parts of a communications controller 17 accordingto the invention. This communications controller 17 is based on acompletely different “architecture” compared to the known communicationscontroller 1 according to FIG. 1. With the communications controller 17according to FIG. 2 the system clock is delivered from a symbol clockretrieving circuit 18 which the system clock achieved in this waydelivers to all processor modules 19-22 integated for a paralleloccuring processing of data.

The data decoder indicated with numeral 13 delivers decoded data to theprocessor modules 19-22, which after each reception of data over theline indicated with numeral 24 will decode these data, process them andform answers. Immediate after the last bit of the received data sequence(data frame) has been decoded the transmission of answering, data overthe line indicated with numeral 25 can be started. In this way not onlythe duration between the reception of the input signal and theirradiation of the output signal of the transponder is considerablyshortened, but because of the considerably reduced clock frequency ofthe system clock of the transponder—also the load of the battery of thetransponder is reduced in a considerable extent.

1. Method for processing of encoded information by a battery-poweredactive transponder, provided for the application within a transpondersystem for the wireless payment of road toll, comprising: receivingmodulated microwave radiation of preset frequency by the transponderover the antenna and for obtaining an input signal demodulated forobtaining a binary input data sequence, feeding said binary input datasequence to a digital processor (microcontroller) operated by aprocessing clock of preset clock frequency for decoding and generatingof a binary output data sequence, forming an output signal from ananswer to the received input signal within a certain duration andtransmitting over the antenna of the transponder, characterized in thatfor reducing the load of the battery of the transponder by thepulse-like occurring current demand of the processor with at the sametime a relative short duration between the receiving of the input signaland the irradiating of the output signal data, the decoded input datasequence are processed by the processor parallel and with a relative lowclock frequency.
 2. Method according to claim 1, characterized in thatthe parallel occurring processing of data of the decoded input datasequence is realized with a much lower clock frequency, and only afraction of that clock frequency, compared to a clock frequency of about10 MHz and higher with a serial occurring processing according to thestate-of-the-art.
 3. Method according to claim 1, characterized in thatthe parallel occurring processing of data of the decoded input datasequence is realized with a clock frequency which is derived from theclock of the symbol timing generator by retrieving of a plurality ofsucceeding timing pulses of the symbol clock from the input datasequence and corresponding to the clock frequency of the symbol clock.4. Method according to claim 3, characterized in that for forming of aclock frequency either derived from the clock frequency of the symbolclock or corresponding to this clock frequency an electronic PLL-circuit(phase locked loop) is applied.
 5. Method according to claim 1,characterized in that the parallel occurring processing of data of thedecoded input data sequence is realized bit-by-bit.
 6. Communicationscontroller (17) for a battery-powered active transponder provided forthe application within a transponder system for the wireless payment ofroad toll, whereby the transponder over an antenna receives modulatedmicrowave radiation of preset frequency for obtaining an input signalwhich is demodulated for obtaining a binary input data sequence, whichthen is fed to a digital processor (17) (microcontroller) operated by aprocessing clock of preset clock frequency for decoding and generatingof a binary output data sequence, from which within a certain durationas an answer to the received input signal an output signal is formed,which is transmitted over the antenna of the transponder, characterizedby a plurality of processor modules (19-22) of the processor (17) whichare integrated to a processing unit realizing the parallel occurringprocessing of data of the decoded input data sequence and are operatedby a timing generator (symbol clock retrieving circuit 18) with arelative low clock frequency of the processing clock rate. 7.Communications controller (17) according to claim 6, characterized inthat as timing generator for generating a processing clock rate for thementioned processor modules (19-22) an electronic circuit is providedfor retrieving the clock frequency of the symbol clock from the inputsignal.
 8. Communications controller (17) according to claim 7,characterized in that for generating of a processing clock rate for thementioned processor modules (19-22) with a clock frequency derived fromthe clock frequency of the symbol clock, corresponding to the symbolclock, a PLL-circuit (phase locked loop) is applied.
 9. Communicationscontroller (17) according to claim 6, characterized in that theprocessor modules (19-22) are dimensioned for a bit-by-bit processing ofdata of the decoded input data sequence